Tantrum tempering

When my daughter was about 4 she would throw terrible tantrums.
One night I got her to stay on her bed (I'm not sure how, no physical constraints were used) and setup a video camera to tape her episode. It lasted 20 minutes. Once she finally calmed down, I mad her stay on her bed and watch the entirety of the video.
After than, we talked.
She told me what she saw and how she felt about the way she acted.
I told her that now she understands how we see her when she acts that way. I asked her if she wanted us to show that video to Grandma and Grandpa (I'm not above playing dirty). She obviously didn't. Ever since then she only needed a gentle reminder to snap back into shape.
She hasn't always been perfect since, but at least we didn't get the all-out trauma-fest.